1. Field of the Invention
The present invention relates to a method of generating an alert for a walkie-talkie, more specifically, a method used in the walkie-talkie for generating a warning signal when the walkie-talkie will be out of communicable distance.
2. Description of the Prior Art
A continuous tone-coded squelch system (CTCSS) has been widely applied to wireless transmission, and is used to let a plurality of users communicate with each other within a predetermined communication area. The CTCSS adopts a low-frequency CTCSS tone signal to distinguish signals transmitted via the same physical channel. For instance, a prior art walkie-talkie utilizes the CTCSS to achieve group communication. Please refer to FIG. 1, which is a schematic diagram showing frequency bands used by the prior art CTCSS. As shown in FIG. 1, a band ranging from 62.5 Hz to 250 Hz is used to transmit the above-mentioned low-frequency CTCSS tone signal, and another band ranging from 300 Hz to 3.4 KHz is used to transmit speech signals spoken by a user. The operation of the CTCSS is described as follows. With regard to the prior art walkie-talkie, 14 channels P1-P14 generally are adopted to carry signals, and the 14 channels are physical channels. In addition, 38 CTCSS tone signals T1-T38 individually corresponding to different frequencies are used. One of the 38 CTCSS tone signals T1-T38 annexed to one physical channel generates a specific logical channel, and the 14 physical channels are capable of forming 532 (14*38) logical channels in total. When a speaker sets the walkie-talkie with a physical channel P1 and a desired CTCSS tone signal T1, that is, the logical channel set by the speaker becomes P1 (T1). After the speaker presses a push-to-talk (PTT) button on the walkie-talkie, the speaker is capable of outputting speech signals via the walkie-talkie toward the predetermined communication area specified by the walkie-talkie. If there are three listeners in the predetermined communication area, and the three listener set their own logical channels as P1 (T1), P1 (T38), P2 (T1) respectively. For the first listener with a logical channel P1 (T1), because his walkie-talkie receives and transmits signals through the physical channel P1, the walkie-talkie of the first listener will start receiving speech signals spoken by the speaker. In addition, the walkie-talkie of the first listener judges that the CTCSS tone signal used by the speaker is T1. In other words, the speaker and the first listener both adopt the same logical channel P1 (T1). Therefore, the walkie-talkie of the first listener then outputs the received speech signals via an audio speaker. The first listener is capable of hearing the speech signals spoken by the speaker. For the second listener with a logical channel P1 (T38), because his walkie-talkie receives and transmits signals through the physical channel P1, the walkie-talkie of the second listener will start receiving speech signals spoken by the speaker. However, the walkie-talkie of the second listener judges that the CTCSS tone signal used by the speaker is not T1, but T38. In other words, the speaker and the second listener adopt different logical channels P1 (T1) and P1 (T38). Therefore, the walkie-talkie of the second listener then does not output the received speech signals via an audio speaker. The second listener cannot hear the speech signals spoken by the speaker. For the third listener with a logical channel P2 (T1), because his walkie-talkie receives and transmits signals through the physical channel P2, the walkie-talkie of the third listener and that of the speaker use different physical channels. With the unmatched physical channel, the walkie-talkie of the third listener cannot acknowledge an adequate signal strength indicated by a received signal strength indicator (RSSI). Therefore, the walkie-talkie of the third listener will not receive any speech signals spoken by the speaker. That is, no speech signal is played by an audio speaker of the walkie-talkie. The second and third listeners cannot hear any speech signals spoken by the speaker, that is, the walkie-talkies of the second and third listeners both detect the CTCSS tone signal related to the received speech signals for actuating a signal squelch function. To sum up, only the users using the same logical channel can communicate with each other to achieve group communication.
Please refer to FIG. 2, which is a block diagram of a prior art walkie-talkie 10. The walkie-talkie 10 has an antenna 11, a transceiver 12, a selector 14, a processor 16, a speaker 17, a microphone 18, and a speech signal processor 20. The walkie-talkie 10 can receive and transmit radio frequency (RF) signals through the antenna 11. With regard to receiving RF signals, the transceiver 12 converts the high-frequency RF signal into a low-frequency baseband signal Rx, and transmits the baseband signal Rx to the selector 14. The selector 14 then outputs the baseband signal Rx from an output port A. The processor 16 determines frequency of a CTCSS tone signal according to the received baseband signal Rx. Generally speaking, the processor 16 has a low-pass filter (LPF) for extracting signals with frequencies ranging from 62.5 Hz to 250 Hz, and then the processor 16 judges the CTCSS tone signal related to the baseband signal Rx to decide whether the walkie-talkie 10 and the baseband signal Rx use the same logical channel. If the walkie-talkie 10 and the baseband signal Rx use the same logical channel, the processor 16 activates the speaker 17 to proceed following signal output operation. That is, the speech signal processor 20 has two analog filter circuits for extracting signals with frequencies ranging from 300 Hz to 3.4 KHz, and the extracted signals are played by the speaker 17. On the contrary, if the walkie-talkie 10 and the baseband signal Rx use different logical channels, the processor 16 does not actuate the speech signal processor 20 and the speaker 17. The walkie-talkie 10, therefore, does not output any speech signals transmitted by unmatched logical channels. With regard to transmitting RF signals, when the user presses the PTT button, the selector 14 will chose the input port B, and the processor 16 simultaneously actuates the microphone 18. Therefore, the speech signals spoken by the user are inputted into the speech signal processor 20. As mentioned above, the speech signal processor 20 uses filter circuits to extract signals with frequencies ranging from 300 Hz to 3.4 KHz, and the speech signal processor 20 outputs the extracted signals to the CTCSS encoder 18. Based on a CTCSS code (CTCSS tone signal with a specific frequency) set in the walkie-talkie 10, the processor 16 adds a corresponding CTCSS tone signal in the extracted signals outputted from the speech signal processor 20 for forming a baseband signal Tx. In the end, the transceiver 12 converts the low-frequency baseband signal Tx into a high-frequency RF signal, and the RF signal is then outputted via the antenna 11.
Generally speaking, because the radio signal easily is obstructed by obstacles, such as trees, thick leaf and building, or particle, such as steam and dust, which can limit the conversationscope for the walkie-talkie. As for the user, although the common walkie talkies are given a recommend conversation scope, but these scopes are estimation values. Under different environments, in fact, the really conversation scopes are not fixed, meaning that the user cannot know the real conversation scopes with each other. Therefore, unconsciously, a bad communication quality is caused by terrain and environmental factor.
It is therefore a primary objective of the claimed invention to provide a method used in a walkie-talkie for generating a warning signal while leaving a conversation distance to solve the aforementioned problem.
Briefly summarized, the claimed invention provides a method for a walkie-talkie comprising providing a detector and a timer; using the timer to count time; using the detector to determine whether the strength of a radio frequency (RF) signal which includes a standard CTCSS tone received by the walkie-talkie is larger than a predetermined value; using the detector to determine whether the strength of a RF signal which includes a non-standard CTCSS tone received by the walkie-talkie is larger than the predetermined value; if so, resetting the timer; and issuing a warning signal when the time counted by timer reaches a predetermined time.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the invention, which is illustrated in the various figures and drawings.